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The traditional Magnetic Bead Separation is a permanent magnet block. The test tube is placed next to the magnet and the magnetic particles in solution move toward the magnet. This system works for very small volumes, but it is not the most efficient method and problems often arise in larger volumes. The downfall of this geometry is that the permanent magnet is only on one side of the tube, which means that the magnetic particles are only drawn to that one side. The magnetic particles close to the magnet will experience a higher force than the magnetic particles farthest away from the magnet. Magnetic force decreases as distance from the magnet increases, so the particles farthest away might not feel any force if the magnetic strength is not great enough.

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One solution is to find a bigger magnet. As the magnetic force decreases very fast with the distances, is not easy (and sometimes impossible) to allow the particle farthest away to feel a sufficient magnetic force. Even so, the particles closest to the magnet will experience an extremely large magnetic force. In cell separation protocols this can be detrimental to the cells because the high magnetic force can destroy the membrane and cause cell death. This is less of a concern in DNA purification because there are no live cells to worry about, but the separation efficiency is still compromised by the irreversible aggregation of magnetic particles closest to the retention area.  Additionally, the separation time can be painfully long due to uneven forces throughout the working volume.

Advanced Magnetic Bead Separation systems are engineered to produce a constant magnetic force throughout the working volume. This means that the magnetic force felt by a magnetic particle does not vary greatly with location. Ideally, all particles within the sample will experience a comparable magnetic force. This translates to faster separation times and greater separation efficiency because all of the particles will experience an optimal magnetic force. All particles are captured within a comparable time-scale because there are no particles left behind, and irreversible aggregation of particles is avoided since it is not necessary to increase retention force to capture the farthest beads. These advanced biomagnetic separation systems are carefully designed with optimized geometry, magnetic field strength, shape, and gradient. They are also equipped with real-time quantitative software that provides optical monitoring of the separation process. This software provides the additional benefit of standard curves to compare separation efficiency across experiments, which is critical when optimizing a new separation protocol. Also, this added feature takes the guesswork out of the separation process. It is easy to see when the separation is complete, and a typical separation requires only a few short minutes.

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Advanced biomagnetic separation systems are particularly beneficial for nucleic acid isolation because of their short separation times and high yield. Short separation times are important when analyzing a large number of samples. Higher yield is very desirable, especially when isolating DNA or RNA from a rare cell type and a minimum concentration of nucleic acid must extracted for use in qPCR or sequencing.

It is important to remember that the magnetic forces play a fundamental role in the magnetic separation process. When faced with difficulties in their separation strategy many people might first think that their choice of magnetic particle, coating, or functionalization chemistry is at fault. However, the root of long separation times and poor yield often lies in a poorly designed separation system. An advanced magnetic separation system can save frustration, time, and money.

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Lluis M. Martínez | SEPMAG Chief Scientific Officer

Founder of SEPMAG, Lluis holds a PhD in Magnetic Materials by the UAB. He has conducted research at German and Spanish academic institutions. Having worked in companies in Ireland, USA and Spain, he has more than 20 years of experience applying magnetic materials and sensors to industrial products and processes. He has filed several international patents on the field and co-authored more than 20 scientific papers, most of them on the subject of magnetic particle movement.

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